The present invention relates generally to voltage regulation for integrated circuits and, more particularly, to an improved voltage regulator and method using high density integrated inductors and capacitors for radio frequency suppression.
Business and consumers use a wide array of wireless devices, including cell phones, wireless local area network (LAN) cards, global positioning system (GPS) devices, electronic organizers equipped with wireless modems, and the like. The increased demand for wireless communication devices has created a corresponding demand for technical improvements to such devices. Generally speaking, more and more of the components of conventional radio receivers and transmitters are being fabricated in a single integrated circuit (IC) package. In order to simplify single chip designs and to make each design suitable for as many applications as possible, much emphasis has been placed on developing on-chip voltage regulators.
Conventional integrated circuits include high frequency oscillators, such as crystal oscillators or voltage-controlled oscillators, which require high stability and low phase noise. Thus, these oscillators generally cannot tolerate noise riding on their supply rails and bias lines. However, the increased integration of components onto a single chip typically results in a noisier environment.
One solution to the problems of excess noise and transient undulation in integrated circuits has been to use bypass capacitors and voltage regulators. Low dropout voltage regulators are used to track out low frequency signals and a bypass capacitor is used to shunt some high frequency components to the rail.
However, bypass capacitors generally cannot redirect an acceptable amount of the high frequency noise, such as radio frequency noise, that is typically associated with communication devices. In addition, because the high frequency components are shunted to the rail by the bypass capacitor, these components may end up as a disturbance elsewhere in the integrated circuit.
One solution to this problem involves the addition of an external inductor. The impedance of the inductor increases at high frequencies, so high frequency noise can be greatly attenuated, blocked or dissipated as heat as it traverses the inductor. However, a problem associated with this solution is that the inductor is typically located at the end of the voltage regulation chain. As a result of this, the DC voltage drop across the inductor could result in large output voltage variation due to load current changes and component tolerance, thereby defeating the original purpose of the voltage regulator.
Another solution to the problem has been to boost up the bandwidth of an error amplifier in the regulator system. However, problems with this solution include increased power consumption, reduced gain, and reduced stability margin. In addition, there is a limit to how much the bandwidth may be boosted. Generally, a gigahertz, or even a hundreds of megahertz, bandwidth amplifier is not feasible in a regulator system. Moreover, having a wider bandwidth amplifier causes the feedback system to execute rapid, nearly constant corrections. Thus, with large input or power supply perturbations, the feedback system may generate noise, may overcorrect or undercorrect, and may consume excessive power.
Other problems with conventional voltage regulators include an inability to provide internal compensation not only due to the load being an unknown parameter, but more importantly because internal compensation (of the error amplifier) often exacerbates power supply rejection ratio problems and makes high frequency suppression performance even worse. Therefore, in order to provide compensation, large and expensive external load capacitors are typically employed as compensation components.
In accordance with the present invention, an improved voltage regulator and method are provided that substantially eliminate or reduce disadvantages and problems associated with conventional systems and methods. In particular, on-chip inductors are integrated in the feedback loop of a voltage regulator to remove high frequencies without compromising the regulated output level.
According to one embodiment of the present invention, a voltage regulator formed on an integrated circuit is provided. The voltage regulator includes an amplifier and a feedback circuit. The amplifier is operable to receive a reference voltage and a feedback voltage. The amplifier is also operable to generate a regulated output voltage based on the reference voltage and the feedback voltage. The feedback circuit, which is coupled to the amplifier, is operable to generate the feedback voltage. The feedback circuit includes an inductor-capacitor network. The inductor-capacitor network is operable to remove high frequencies from the output voltage.
According to yet another embodiment of the present invention, a method for regulating an output voltage for a voltage regulator formed on an integrated circuit is provided. The method includes providing an output voltage to a feedback circuit. The feedback circuit includes an inductor-capacitor network. High frequencies are removed from the output voltage with the inductor-capacitor network of the feedback circuit. A feedback voltage is generated with the feedback circuit. The feedback voltage is based on the output voltage. The output voltage is regulated based on the feedback voltage.
According to yet another embodiment of the present invention, a method for internally compensating a voltage regulator formed on an integrated circuit is provided. The method includes coupling a feedback circuit to an amplifier. The feedback circuit includes an inductor-capacitor network. The amplifier is operable to regulate an output voltage for the voltage regulator based on a feedback voltage from the feedback circuit. The output voltage is provided to the feedback circuit. Stability of the output voltage is compensated with the inductor-capacitor network of the feedback circuit. The feedback voltage is generated with the feedback circuit based on the output voltage.
Technical advantages of one or more embodiments of the present invention include providing an improved voltage regulator. In a particular embodiment, on-chip inductors are integrated in the feedback loop of a voltage regulator. As a result, high frequencies are removed without compromising the regulated output level. In addition, on-chip capacitors are integrated in the feedback loop, enabling the voltage regulator to be internally compensated. This minimizes cost and board space requirements for the voltage regulator as compared to voltage regulators using large external load capacitors for loop stability.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.